Physical Sciences and Mathematics Commons^™

Phenyl-Substituted Siloxane Hybrid Gels That Soften Below 140[Degrees]C, Andrei Jitianu, Glenn Amatucci, Lisa C. Klein

Publications and Research

A characteristic of so-called melting gels is that the gels, which are rigid at room temperature, are able to soften and resoften at temperatures around 110 [degrees]C. However, after consolidation at temperatures higher than 150 [degrees]C, the gels no longer resoften. Two systems of melting gels were investigated: phenyltrimethoxysilane (PhTMS)–diphenyldimethoxysilane (DPhDMS) and phenyltriethoxysilane (PhTES)–diphenyldiethoxysilane (DPhDES). The influence of disubstituted versus monosubstituted alkoxide on the softening behavior and the temperature of decomposition was studied. The consolidation temperature increased as the amount of disubstituted alkoxide increased, while the decomposition temperature increased only slightly. In general, the ethoxy-containing gels (maximum at 150[degrees]C) consolidated …

Interconnections Of Nonlinear Systems Driven By L₂-Itô Stochastic Processes, Luis A. Duffaut Espinosa

Electrical & Computer Engineering Theses & Dissertations

Fliess operators have been an object of study in connection with nonlinear systems acting on deterministic inputs since the early 1970's. They describe a broad class of nonlinear input-output maps using a type of functional series expansion, but in most applications, a system's inputs have noise components. In such circumstances, new mathematical machinery is needed to properly describe the input-output map via the Chen-Fliess algebraic formalism. In this dissertation, a class of L₂-Itô stochastic processes is introduced specifically for this purpose. Then, an extension of the Fliess operator theory is presented and sufficient conditions are given under which …

Continuous And Smooth Potential Energy Surface For Conductorlike Screening Solvation Model Using Fixed Points With Variable Areas, Peifeng Su, Hui Li

Department of Chemistry: Faculty Publications

Rigorously continuous and smooth potential energy surfaces, as well as exact analytic gradients, are obtained for a conductorlike screening solvation model (CPCM, a variant of the general COSMO) with Hartree–Fock (RHF, ROHF, UHF, and MCSCF) and density functional theory (R-DFT, RO-DFT, and U-DFT) methods using a new tessellation scheme, fixed points with variable areas (FIXPVA). In FIXPVA, spheres centered at atoms are used to define the molecular cavity and surface. The surface of each sphere is divided into 60, 240, or 960 tesserae, which have positions fixed relative to the sphere center and areas scaled by switching functions of their …

Smooth Potential Energy Surface For Cavitation, Dispersion, And Repulsion Free Energies In Polarizable Continuum Model, Yali Wang, Hui Li

Department of Chemistry: Faculty Publications

The fixed points with variable areas [FIXPVA (Ref. 1)] tessellation scheme is used to obtain smooth potential energy surfaces for the cavitation G_cav, dispersion G_dis, and repulsion G_rep free energies in the polarizable continuum model (PCM). It is shown that FIXPVA can reproduce the standard GEPOL (Ref. 4) results to within 1 kcal/mol.

A New Peroxide Fragmentation: Efficient Chemical Generation Of 1O2 In Organic Media, Patrick Dussault, Prasanta Ghorai

Department of Chemistry: Faculty Publications

Monoactivated derivatives of 1,1-dihydroperoxides undergo an unprecedented base-promoted fragmentation to efficiently generate singlet oxygen (¹O₂) in anhydrous organic solvents.

Absence Of Spin Liquid Behavior In Nd3ga5sio14 Using Magneto-Optical Spectroscopy, X. S. Xu, T. V. Brinzari, S. Mcgill, H. D. Zhou, C. R. Wiebe, J. L. Musfeldt

Xiaoshan Xu Papers

We measured the low-lying crystal field levels of Nd³⁺ in Nd₃Ga₅SiO₁₄ via magneto-optical spectroscopy and employed the extracted energies, magnetic moments, and symmetries to analyze the magnetic properties and test the spin liquid candidacy of this material. The exchange interaction is surprisingly small, a discovery that places severe constraints on models used to describe the ground state of this system. Further, it demonstrates the value of local-probe photophysical techniques for rare-earthcontaining materials where bulk property measurements can be skewed by low-lying electronic structure.

Igc Fabrication And Tem Characterization Of Mn Nanoparticles, Xingzhong Li, Zhiguang Sun, David J. Sellmyer

David Sellmyer Publications

The reason for the enormous interest in nanomaterials is because they display unique and superior properties that are generally unavailable in conventional macroscopic materials. Gleiter and coworkers [1] first generated a novel solid structure with gas-like disorder, in addition to long-range order (crystalline and quasicrystalline solids) and short-range order (amorphous/glassy solids). Inert-gas condensation (IGC) is a well established nanoparticle production technique [2-4]. Figure 1 shows an IGC system equipped with magnetron sputter source and mass selector that was used in the present work. The ability to control the process parameters to fabricate metal nanoparticles with tailored size, shape, and properties …

Temporal Lenses For Attosecond And Femtosecond Electron Pulses, Shawn A. Hilbert, Cornelis J. Uiterwaal, Brett E. Barwick, Herman Batelaan, Ahmed H. Zewail

C.J.G.J. Uiterwaal Publications

Here, we describe the ‘‘temporal lens’’ concept that can be used for the focus and magnification of ultrashort electron packets in the time domain. The temporal lenses are created by appropriately synthesizing optical pulses that interact with electrons through the ponderomotive force. With such an arrangement, a temporal lens equation with a form identical to that of conventional light optics is derived. The analog of ray diagrams, but for electrons, are constructed to help the visualization of the process of compressing electron packets. It is shown that such temporal lenses not only compensate for electron pulse broadening due to velocity …

Anisotropic Magnetoresistance And Planar Hall Effect In Epitaxial Films Of La0.7Ca0.3Mno3, N. Naftalis, Y. Bason, J. Hoffman, X. Hong, C. H. Ahn, L. Klein

Xia Hong Publications

We measured the anisotropic magnetoresistance (AMR) and the planar Hall effect (PHE) in a [001] oriented epitaxial thin film of La_0.7Ca_0.3MnO₃ (LCMO) as a function of magnetic field, temperature, and current direction relative to the crystal axes. We find that both AMR and PHE in LCMO depend strongly on the current orientation relative to the crystal axes, and we demonstrate the applicability of AMR and PHE equations based on a fourth order magnetoresistance tensor consistent with the film symmetry.

High-Mobility Few-Layer Graphene Field Effect Transistors Fabricated On Epitaxial Ferroelectric Gate Oxides, X. Hong, A. Posadas, K. Zou, C. H. Ahn, J. Zhu

Xia Hong Publications

The carrier mobility μ of few-layer graphene (FLG) field-effect transistors increases tenfold when the SiO₂ substrate is replaced by single-crystal epitaxial Pb(Zr_0.2Ti_0:8)O₃ (PZT). In the electron-only regime of the FLG, μ reaches 7 X 10⁴ cm² / Vs at 300 K for n = 2.4 X 10¹²=cm², 70% of the intrinsic limit set by longitudinal acoustic (LA) phonons; it increases to 1.4 X 10⁵ cm² / Vs at low temperature. The temperature-dependent resistivity p(T) reveals a clear signature of LA phonon scattering, yielding …

Quantum Scattering Time And Its Implications On Scattering Sources In Graphene, X. Hong, K. Zou, J. Zhu

Xia Hong Publications

We determine the quantum scattering time T_q in six graphene samples with mobility of 4 400<μ <17 000 cm² /V s over a wide range of carrier density (1.2<n<6X10¹²/cm2). T_q derived from Shubnikov–de Haas oscillation ranges ~25–74 fs, corresponding to a single-particle level broadening of 4.5–13 meV. The ratio of the transport to quantum scattering time T_t /T_q spans 1.5–5.1 in these samples, which can be quantitatively understood combining scattering from short-ranged centers and charged impurities located within 2 nm of the graphene sheet. Our results suggest that charges residing on the SiO …

Spatial Variations In Local Switching Parameters Of Ferroelectric Random Access Memory Capacitors, D. Wu, I. Kunishima, S. Roberts, Alexei Gruverman

Alexei Gruverman Publications

Spatially resolved studies of the switching behavior of micrometer scale Pb(Zr,Ti)O₃ capacitors have been performed by piezoresponse force microscopy (PFM). PFM spectroscopy and bias-dependent imaging of domain patterns have been used to investigate variability in local switching parameters and address the capacitor scaling effect on switching. It was found that average coercive voltage and imprint bias are independent of capacitor size and are similar to the corresponding parameters obtained by polarization hysteresis measurements. This can be attributed to the slow switching kinetics during quasistatic PFM measurements. The obtained results demonstrate a possibility of testing the submicron capacitors in real …

Electron Attachment To Cl2 From 300 To 1100 K: Experiment And Theory, Jeffrey Friedman, Thomas Miller, Linda Schaffer, A. A. Viggiano, Ilya I. Fabrikant

Ilya Fabrikant Publications

Rate constants for dissociative electron attachment to Cl₂ have been measured from 300 to 1100 K in a high-temperature flowing-afterglow Langmuir-probe apparatus. R-matrix calculations have been carried out which compare well with the present measurements with possible deviation at the highest temperatures. The attachment rate constants do not show Arrhenius behavior. The temperature dependence of the calculated rate constants for successive vibrational levels provides insight as to this behavior. While the lowest vibrational level of Cl₂ dominates attachment at low temperatures, the rate constant is not flat with temperature because of the p-wave character of the …

High-Energy Laser-Accelerated Electron Beans For Long-Range Interrogation, Nathaniel Cunningham, Sudeep Banerjee, Viswanathan Ramanathan, Nathan D. Powers, Nathan A. Chandler-Smith, Randy Vane, David Schultz, Sara Pozzi, Shaun Clark, James Beene, Donald Umstadter

Donald Umstadter Publications

We are studying the use of 0.1 - 1.0 GeV laser-accelerated electron beams as active interrogation probes for long-standoff radiography or nuclear activation of concealed special nuclear material. Use of beams in this energy range is largely unexplored, but such beams could provide notable advantages over lower-energy beams and x-rays. High-energy laser-accelerated electrons exhibit large penetration range through air and solids, and low beam divergence for both direct beams and secondary Bremsstrahlung x-rays. We present laboratory measurements of radiography and activation using the high power Diocles laser system at the University of Nebraska, as well as MCNP and GEANT Monte …

Magnetism Of Chromia From First-Principles Calculations, Siqi Shi, Aleksander L. Wysocki, Kirill D. Belashchenko

Department of Physics and Astronomy: Faculty Publications

The electronic structure and magnetism of chromia (corundum-type Cr₂O_{3) are studied using full-potential first-principles calculations. The electronic correlations are included within the LSDA+U method. The energies of different magnetic configurations are very well fitted by the Heisenberg Hamiltonian with strong exchange interaction with two nearest neighbors and additional weak interaction up to the fifth neighbor shell. These energies are insensitive to the position of the oxygen states, indicating that magnetism in Cr2O3 is dominated by direct exchange. The Néel temperature is calculated using the pair-cluster approximation for localized quantum spins of magnitude 3/2. …}

Nonlinear Laser Energy Depletion In Laser-Plasma Accelerators, Bradley Allan Shadwick, Carl B. Schroeder, Eric Esarey

Department of Physics and Astronomy: Faculty Publications

Energy depletion of intense, short-pulse lasers via excitation of plasma waves is investigated numerically and analytically. The evolution of a resonant laser pulse proceeds in two phases. In the first phase, the pulse steepens, compresses, and frequency redshifts as energy is deposited in the plasma. The second phase of evolution occurs after the pulse reaches a minimum length at which point the pulse rapidly lengthens, losing resonance with the plasma. Expressions for the rate of laser energy loss and rate of laser redshifting are derived and are found to be in excellent agreement with the direct numerical solution of the …

First-Principles Analysis Of Spin-Disorder Resistivity Of Fe And Ni, Aleksander L. Wysocki, Renat F. Sabirianov, Mark Van Schilfgaarde, Kirill D. Belashchenko

Department of Physics and Astronomy: Faculty Publications

Spin-disorder resistivity of Fe and Ni and its temperature dependence are analyzed using noncollinear density functional calculations within the supercell method. Different models of thermal spin disorder are considered, including the mean-field approximation and the nearest-neighbor Heisenberg model. If the local moments are kept frozen at their zero-temperature values, very good agreement with experiment is obtained for Fe but for Ni the resistivity at elevated temperatures is significantly overestimated. Agreement with experiment for Fe is improved if the local moments are made self-consistent. The effect of short-range order on spindisorder resistivity is more pronounced in Ni compared to Fe but …

Prediction Of Electrically Induced Magnetic Reconstruction At The Manganite/Ferroelectric Interface, John D. Burton, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

The control of magnetization via the application of an electric field, known as magnetoelectric coupling, is among the most fascinating and active research areas today. In addition to fundamental scientific interest, magnetoelectric effects may lead to new device concepts for data storage and processing. There are several known mechanisms for magnetoelectric coupling that include intrinsic effects in single-phase materials, strain-induced coupling in two-phase composites, and electronically driven effects at interfaces. Here we explore a different type of magnetoelectric effect at a ferromagnetic-ferroelectric interface: magnetic reconstruction induced by switching of electric polarization.

Oxide Tunnel Junctions Supporting A Two-Dimensional Electron Gas, John D. Burton, Julian P. Velev, Evgeny Y. Tsymbal

Evgeny Tsymbal Publications

The discovery of a two-dimensional electron gas (2DEG) at the interface between insulating oxides has led to a well-deserved level of excitement due to possible applications as “in-plane” all-oxide nanoelectronics. Here we expand the range of possibilities to the realm of “out-of-plane” nanoelectronics by examining such all-oxide heterostructures as barriers in tunnel junctions.

Relating Groundwater To Seasonal Wetlands In Southeastern Wisconsin, Usa, John D. Skalbeck, Donald M. Reed, Randall J. Hunt, Jamie D. Lambert

United States Geological Survey: Staff Publications

Historically, drier types of wetlands have been difficult to characterize and are not well researched. Nonetheless, they are considered to reflect the precipitation history with little, if any, regard for possible relation to groundwater. Two seasonal coastal wetland types (wet prairie, sedge meadow) were investigated during three growing seasons at three sites in the Lake Michigan Basin, Wisconsin, USA. The six seasonal wetlands were characterized using standard soil and vegetation techniques and groundwater measurements from the shallow and deep systems. They all met wetland hydrology criteria (e.g., water within 30 cm of land surface for 5% of the growing season) …

Factors Associated With Duck Use Of Impounded And Natural Wetlands In Western South Dakota, Jane E. Austin, Deborah A. Buhl

The Prairie Naturalist

Many wetlands in the northern Great Plains west of the Missouri River are stock ponds, created by impoundment of natural drainages or excavation of existing wetlands to provide water for livestock or improve habitat for waterfowl. We evaluated factors influencing use of wetlands by breeding duck pairs and broods relative to modification, water regime, size, and hydrological location on United States Forest Service lands within the Grand River National Grassland in northern South Dakota (2003 and 2004). Responses for both indicated pairs and broods were related positively to wet area, total wetland area within 4 km, emergent edge cover, and …

Implications For The Dynamic Health Of A Glacier From Comparison Of Conventional And Reference-Surface Balances, W. D. Harrison, L. H. Cox, R. Hock, R. S. March, E. C. Pettit

United States Geological Survey: Staff Publications

Conventional and reference-surface mass-balance data from Gulkana and Wolverine Glaciers, Alaska, USA, are used to address the questions of how rapidly these glaciers are adjusting (or ‘responding’) to climate, whether their responses are stable, and whether the glaciers are likely to survive in today’s climate. Instability means that a glacier will eventually vanish, or at least become greatly reduced in volume, if the climate stabilizes at its present state. A simple non-linear theory of response is presented for the analysis. The response of Gulkana Glacier is characterized by a timescale of several decades, but its stability and therefore its survival …

A Multi-Step Nmr Screen For The Identification And Evaluation Of Chemical Leads For Drug Discovery, Kelly A. Mercier, Matthew D. Shortridge, Robert Powers

Department of Chemistry: Faculty Publications

A multi-step NMR based screening assay is described for identifying and evaluating chemical leads for their ability to bind a target protein. The multi-step NMR assay provides structure-related information while being an integral part of a structure based drug discovery and design program. The fundamental principle of the multi-step NMR assay is to combine distinct 1D and 2D NMR techniques, in such a manner, that the inherent strengths and weakness associated with each technique is complementary to each other in the screen. By taking advantage of the combined strengths of 1D and 2D NMR experiments, it is possible to minimize …

Androgen-Stimulated Udp-Glucose Dehydrogenase Expression Limits Prostate Androgen Availability Without Impacting Hyaluronan Levels, Qin Wei, Robert Galbenus, Ashraf Raza, Ronald Cerny, Melanie A. Simpson

Ronald Cerny Publications

UDP-glucose dehydrogenase (UGDH) oxidizes UDP-glucose to UDP-glucuronate, an essential precursor for production of hyaluronan (HA), proteoglycans, and xenobiotic glucuronides. High levels of HA turnover in prostate cancer are correlated with aggressive progression. UGDH expression is high in the normal prostate even though HA accumulation is virtually undetectable. Thus, its normal role in the prostate may be to provide precursors for glucuronosyltransferase enzymes, which inactivate and solubilize androgens by glucuronidation. In this report, we quantified androgen dependence of UGDH, glucuronosyltransferase, and HA synthase expression. Androgen dependent and independent human prostate cancer cell lines were used to test the effects of UGDH …

A Lacustrine Carbonate Record Of Holocene Seasonality And Climate, Chad A. Wittkop, Jane L. Teranes, Walter E. Dean, Thomas P. Guilderson

United States Geological Survey: Staff Publications

Annually laminated (varved) Holocene sediments from Derby Lake, Michigan, display variations in endogenic calcite abundance refl ecting a long-term (millennial-scale) decrease in burial punctuated with frequent short-term (decadal-scale) oscillations due to carbonate dissolution. Since 6000 cal yr B.P., sediment carbonate abundance has followed a decreasing trend while organic-carbon abundance has increased. The correlation between organic-carbon abundance and the sum of March-April-October-November insolation has an r² value of 0.58. We interpret these trends to represent a precession-driven lengthening of the Holocene growing season that has reduced calcite burial by enhancing net annual organic-matter production and associated calcite dissolution. Correlations with …

Prevalence Of West Nile Virus In Migratory Birds During Spring And Fall Migration, Robert J. Dusek, Robert G. Mclean, Laura D. Kramer, Sonya R. Ubico, Alan P. Dupuis Ii, Gregory D. Ebel, Stephen C. Guptill

United States Geological Survey: Staff Publications

To investigate the role of migratory birds in the dissemination of West Nile virus (WNV), we measured the prevalence of infectious WNV and specific WNV neutralizing antibodies in birds, principally Passeriformes, during spring and fall migrations in the Atlantic and Mississippi flyways from 2001–2003. Blood samples were obtained from 13,403 birds, representing 133 species. Specific WNV neutralizing antibody was detected in 254 resident and migratory birds, representing 39 species, and was most commonly detected in northern cardinals (Cardinalis cardinalis ) (9.8%, N = 762) and gray catbirds ( Dumetella carolinensis ) (3.2%, N = 3188). West Nile virus viremias …

Paleoceanography Of The Gulf Of Alaska During The Past 15,000 Years: Results From Diatoms, Silicoflagellates, And Geochemistry, John A. Barron, David Bukry, Walter E. Dean, Jason A. Addison, Bruce Finney

United States Geological Survey: Staff Publications

High-resolution records of diatoms, silicoflagellates, and geochemistry covering the past 15,000 years were studied in three cores from the Gulf of Alaska (GOA). Core EW0408-85JC in an oceanic setting on the Kayak Slope displays a paleoceanographic record similar to that at several locations on the California margin during deglaciation. Biologic productivity as reconstructed using geochemical and microfossil proxies increased abruptly during the Bølling–Alleröd (Bø–Al) warm interval (14.7–12.9 cal ka), declined during the Younger Dryas (YD) cold interval (12.9 to 11.7 cal kyr BP), and rose again during the earliest Holocene. At this site, the record after ~11 cal kyr BP …

Possible Sources Of Archaeological Maize Found In Chaco Canyon And Aztec Ruin, New Mexico, Larry Benson, J. R. Stein, H. E. Taylor

United States Geological Survey: Staff Publications

Maize played a major role in Chaco’s interaction with outlying communities in the southern Colorado Plateau. This paper seeks to determine where archaeological corn cobs brought to Chaco Canyon were grown. Strontium-isotope and trace-metal ratios of 180 soil-water and 18 surface-water sites in the Southern Colorado Plateau have revealed possible source areas for some of 37 archaeological corn cobs from Chaco Canyon and 10 archaeological corn cobs from Aztec Ruin, New Mexico. The most probable source areas for cobs that predate the middle-12th-century drought include several Upper Rio Chaco sites (not including Chaco Canyon). There are many potential source areas …

A Robust, Multisite Holocene History Of Drift Ice Off Northern Iceland: Implications For North Atlantic Climate, John T. Andrews, Dennis Darby, Dennis Eberle, Anne E. Jennings, Matthias Moros, Astrid Ogilvie

United States Geological Survey: Staff Publications

An important indicator of Holocene climate change is provided by evidence for variations in the extent of drift ice. A proxy for drift ice in Iceland waters is provided by the presence of quartz. Quantitative xray diffraction analysis of the < 2 mm sediment fraction was undertaken on 16 cores from around Iceland. The quartz weight (wt.)% estimates from each core were integrated into 250-yr intervals between −0.05 and 11.7 cal. ka BP. Median quartz wt.% varied between 0.2 and 3.4 and maximum values ranged between 2.8 and 11.8 wt.%. High values were attained in the early Holocene and minimum values were reached 6–7 cal. ka BP. Quartz wt.% then rose steadily during the late Holocene. Our data exhibit no correlation with counts on haematite-stained quartz (HSQ) grains from VM129-191 west of Ireland casting doubt on the ice-transport origin. A pilot study on the provenance of Fe oxide grains in two cores that cover the last 1.3 and 6.1 cal. ka BP indicated a large fraction of the grains between 1 and 6 cal. ka BP were from either Icelandic or presently unsampled sources. However, there was a dramatic increase in Canadian and Russian sources from the Arctic Ocean ~1 cal. ka BP. These data may indicate the beginning of an Arctic Oscillation-like climate mode.

History Of Wildlife Toxicology, Barnett A. Rattner

United States Geological Survey: Staff Publications

The field of wildlife toxicology can be traced to

the late nineteenth and early twentieth centuries. Initial

reports included unintentional poisoning of birds from

ingestion of spent lead shot and predator control agents,

alkali poisoning of waterbirds, and die-offs from maritime

oil spills. With the advent of synthetic pesticides in the

1930s and 1940s, effects of DDT and other pesticides were

investigated in free-ranging and captive wildlife. In

response to research findings in the US and UK, and the

publication of Silent Spring in 1962, public debate on the

hazards of pollutants arose and national contaminant

monitoring programs were initiated. …